One of these things is not like the other
Sustain specifies a volume level, not a time period. But we can’t simply ignore or get rid of it. Sustain is most certainly a vital part of the way audio envelopes work. Imagine a bland organ sound, but with a nice Leslie effect. The Leslie magic is heard during the sustain portion of the sound. And where would rock guitar be without the sustain pedal?
I'm certainly not calling for the “repeal” of the sustain parameter. After all, Sustain is the only ADSR parameter that comes close to allowing you to set a specific volume level. Unfortunately, that volume control is achieved in a very roundabout and imprecise way.
Well, I want more control. I want to specify the volume level of my sustain. I want to set exactly how loud the sustain level is (in some sort of volume units). Not just a general idea, mind you, like the approximation of the ADSR sliders.
I also want to set exactly how much time my envelope takes to get to the sustain level. I don’t want to set a general “slope”. I want the sustain to kick in in exactly 609 milliseconds. Now how do I do that with ADSR sliders?
By saying all of this, what I’m really asking for is the ability to set precise volumes and times for each stage of the ADSR. The simple idea of setting volumes and times for different envelope stages opens up a new world of possibilities! And the ESQ/SQ80 gives you this ability!
Unlike ADSR, the attack of any natural sound isn’t a simple fade-in slope. It’s more accurate to say that attack is “how much time it initially takes ('Time 1', or 'T1'), to get to the first volume level (Level 1, or 'L1').”
Similarly, for the decay stage (which we could call 'Time 2', or 'T2'), we could do the same thing, specifying exactly when Time 2 will drop down to "volume level 2" (L2).
The beauty of this technique is that we can say exactly how long times 1 and 2 are (in milliseconds), and exactly how loud levels 1 and 2 are. Instead of just guesstimating the whole thing with a single "Attack" or "Decay" slider!
"I see where you're going with this," you say, "but I've found a huge flaw in your time-and-level scheme. I've already set the volume LEVEL (L2) for "Time 2" (which you say is the decay stage). In this scheme, how do I set the sustain volume level (the 'S' slider of the old ADSR)?
That's the beauty of this technique. YOU DON'T HAVE TO!!! You've already set the sustain volume level (L2)!!! No further intervention is required. It's a huge two-fer. You get an amazing degree of time-and-level control that no simple ADSR can match.
These four parameters (T1, L1, T2 and L2) have managed to do--with precision--what three old parameters (ADS...) used to do with rough approximation.
By learning to use Time/Level envelopes, you can do anything ADSR can do, but with unprecedented control, just by mastering one more parameter (T1/L1 T2/L2 vs. ADS...).
Exactly How Long/Exactly How Loud?
Now I'm not saying this is easier than ADSR sliders. Indeed it forces you to think about how loud and how long you want to set each envelop phase.
But for a slight bump in complexity, your sound design jumps from abstraction to precision. (See the following diagram comparing ADSR with T/L pairs).